This invention relates to a wafer cleaning apparatus and a method of cleaning.
More particularly, the present invention relates to wafer cleaning apparatus which is capable of controlling surface charge as it cleans and a method of cleaning.
Polyvinyl alcohol (PVA) sponges or brushes are considered to be a new generation for cleaning a surface such as semiconductor wafers (e.g., silicon, gallium arsenide, silicon carbide, or the like) or memory disc media. Throughout this disclosure, the term xe2x80x9cwaferxe2x80x9d is defined to mean any of the semiconductor wafers, e.g., silicon, gallium arsenide, silicon carbide, or the like, or memory disc media, e.g., glass, aluminum, or other materials well known in the industry, and the term xe2x80x9cwafer is used in place of these items for simplicity of the disclosure.
It is well known that the surface of a wafer, the cleaning brush, and contaminant particles surrounding the cleaning environment of an aqueous system are electrically charged Thus, the utilization of a PVA brush scrubbing process becomes a mechanical and electrical interaction between the surface to be cleaned (the wafer), the PVA brush, and the contaminant particles.
In the process of cleaning wafers, contaminating particles tend to adhere to the surfaces of these media. This adhesion or binding to the surface is due to electrical effects that the particles exhibit between the charge and the surface to be cleaned. It is extremely difficult to clean such a surface unless the contaminant particles to be cleaned and the surrounding environment can be modified to displace the contaminant particles from the surface.
The known cleaning systems used at the present time fail to provide an environment for the removal of charged particles from the surface to be cleaned. These known techniques are rather xe2x80x9chit-or-missxe2x80x9d with no attempt being made to quantitatively regulate the charge upon contaminant particles. Quantitative regulation requires that all the variables utilized in the cleaning process be carefully controlled, e.g., temperature, pH, concentration of surfactants, and most important, the electrical charge upon the surface to be cleaned. Known cleaning systems fail to accomplish the above, since they are not able to quantitatively control the variables mentioned.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide new and improved wafer cleaning apparatus which is is capable of quantitatively controlling surface charges as it cleans and a new and improved method of cleaning wafer surfaces.
Another object of the invention is to provide new and improved apparatus and methods for cleaning wafer surfaces wherein an electrical potential is generated through the surface of a cleaning brush to control the removal of charged particles on the surface.
Briefly, to achieve the desired objects of the instant invention in accordance with a preferred embodiment thereof, provided is wafer cleaning apparatus including a plurality of sponge portions mounted on a common body for movement relative to a surface of a wafer to be cleaned, each sponge portion defining a sponge surface positioned to contact the surface of the wafer. The apparatus further includes means for directing a cleaning fluid flow through each of the sponge portions perpendicular to the sponge surface and onto the surface of the wafer to generate a streaming potential across each of the sponge portions.
To further achieve the desired objects of the instant invention in accordance with a preferred embodiment thereof, a method of cleaning wafers includes providing a plurality of sponge portions mounted on a common body for movement relative to a surface of a wafer to be cleaned, each sponge portion defining a sponge surface positioned to contact the surface of the wafer. A cleaning fluid flow is directed through each of the sponge portions perpendicular to the sponge surface and onto the surface of the wafer to generate a streaming potential across each of the sponge portions. The fluid pressure and pH of the cleaning fluid are adjusted until electrical charges on the sponge surfaces, the wafer, and contaminant particles on the surface of the wafer are all the same electrical sign.